The agrochemical industry is continually seeking methods of improving the growth of plants. Chemicals are typically used to control undesirable species, such as insects or vegetation (e.g. weeds or fungi) and to promote plant growth (e.g., by providing nutrients), thereby improving the growth of plants.
Aside from the direct damage caused by external factors such as plant pests, or the lack of nutrients, the growth of a plant is affected, often detrimentally, by the plant's own responses to external environmental stress factors. When subjected to such stress factors plants display a variety of mechanistic responses as protective measures, with a resultant adverse effect on growth, development, and productivity. Significant losses in quality and yield are commonly observed.
One of the key responses displayed by plants in response to stress is the production of the plant hormone ethylene, which causes a variety of plant physiological effects, such as senescence, inhibition of root growth and inhibition of stem growth. Ethylene also acts to accelerate the process of fruit ripening, flower-opening and leaf abscission. The synthetic plant growth regulator 1-methylcyclopropene (1-MCP) blocks the effects of ethylene and is used commercially to delay fruit-ripening in stored fruits and vegetables and maintaining the freshness of cut flowers, potted flowers, bedding, nursery and foliage plants. The compound is a gas and must be used in enclosed spaces to be effective. It is approved in the USA and elsewhere for use in enclosed spaces, such as greenhouses, store rooms, coolers, enclosed truck trailers, controlled atmosphere food storage facilities, and shipping containers. It is also being developed as post-emergence spray in efforts to protect field crops during extended periods of extreme temperatures, drought and other stresses (Farm Industry News, Jan. 18, 2008).
European patent EP 0,220,514 refers to compositions comprising phytohormones and their use in methods for increasing the quantity and quality of fruits or flowers of plants in horticulture or agriculture. International patent application WO 2005/018319 refers to the application of auxins to the roots of plants by drip irrigation or spray application in order to inhibit insect infestation.
There is a need for additional methods for dealing with the environmental stresses experienced by plants in order to increase their tolerance thereto, and to improve the quality and yield of a plant crop subject to those stresses.